The invention is based on a vehicle brake system for a tractor or towing vehicle as defined herein. Such a brake system is known from German Offenlegungsschrift 36 26 753, which describes a vehicle provided with an axle load transducer. The sensor signal determined by the axle load transducer is dependent on the load carried by the vehicle and is evaluated in an electronic control unit and fed to a yawing moment attenuator as a control variable. The attenuator varies the brake pressure difference beween the brake cylinders of the two sides of the vehicle in such a way that the brake pressure difference in an unloaded vehicle, which is subjected t major yawing and steering moment when braking on a changing surface (for example where there is ice on the edge of the road while the middle of the road has good grip), is kept lower than in a loaded vehicle. Contrarily, vehicles without load-dependent yawing moment control are harder for the driver to control during braking under such conditions, especially if the wheel base is short.